Re: [PATCH v3 0/6] arch, mm/execmem: resolve confusion about set_direct_map_valid_noflush()

[Andrew Morton]

On Thu, 03 Sep 2026 12:28:26 +0300 "Mike Rapoport (Microsoft)" <rppt@xxxxxxxxxx> wrote:

> Recent discussion about implementation of execmem's ROX caches on arm64
> revealed a confusion about how set_direct_map_valid_noflush()
> implemented on different architectures.
> 
> ...
> 
> Implement these adjustments, make execmem always use VM_FLUSH_RESET_PERMS
> and revert set_direct_map_valid_noflush() changes.
> 

Thanks, I updated mm-unstable to this version.

> 
> v3 changes:
> * set VM_FLUSH_RESET_PERMS to allocated area just before flipping the
>   permissions rather than at allocation time
> 

Here's how v3 altered mm.git:


 mm/execmem.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/mm/execmem.c~b
+++ a/mm/execmem.c
@@ -36,7 +36,6 @@ static void *execmem_vmalloc(struct exec
 	unsigned long end = range->end;
 	void *p;
 
-	vm_flags |= VM_FLUSH_RESET_PERMS;
 	if (kasan)
 		vm_flags |= VM_DEFER_KMEMLEAK;
 
@@ -277,6 +276,8 @@ static void *execmem_cache_populate_allo
 	/* fill memory with instructions that will trap */
 	execmem_fill_trapping_insns(p, alloc_size);
 
+	set_vm_flush_reset_perms(p);
+
 	err = set_memory_rox((unsigned long)p, vm->nr_pages);
 	if (err)
 		goto err_free_mem;
@@ -439,6 +440,7 @@ void *execmem_alloc(enum execmem_type ty
 {
 	struct execmem_range *range = &execmem_info->ranges[type];
 	bool use_cache = range->flags & EXECMEM_ROX_CACHE;
+	unsigned long vm_flags = VM_FLUSH_RESET_PERMS;
 	pgprot_t pgprot = range->pgprot;
 	void *p = NULL;
 
@@ -447,7 +449,7 @@ void *execmem_alloc(enum execmem_type ty
 	if (use_cache)
 		p = execmem_cache_alloc(range, size);
 	else
-		p = execmem_vmalloc(range, size, pgprot, 0);
+		p = execmem_vmalloc(range, size, pgprot, vm_flags);
 
 	return kasan_reset_tag(p);
 }
_